Frequently Asked Questions on Quantum Computing…Part 1
Why you should read this?
I think knowing quantum information is both helpful and fun. This FAQ gives you a fair overview of the issues involved in building a quantum computer or quantum communications system and the current challenges.
Here is another thing; Moore’s Law held steady for decades, but it is beginning to falter as miniaturization of processor circuitry gets harder and harder. This challenge makes quantum computing more important as a possible way to continue progress in the industry. As transistors get smaller approaching the nanoscale range quantum mechanical effects start impacting the reliability of circuits. The good thing is that quantum excitations in condensed matter can be harnessed to address computation and storage demands at the atomic level.
Gartner projects evaluation of quantum use cases in the enterprise by 2022, with early quantum applications in deployment by 2026, and commercial use of quantum computing by 2030. Read on and stay ahead of the curve.
What is Quantum Computing (QC)?
Quantum computing harnesses the rules of quantum physics that hold sway over some of the smallest particles in the universe to build devices very different from today’s “classical” computer chips used in smartphones and laptops. Instead of classical computing’s binary bits of information that can only exist in one of two basic states, a quantum computer relies on quantum bits (qubits) that can exist in many different possible states. It’s a bit like having a classical computing coin that can only go “heads” or “tails” versus a quantum computing marble that can roll around and take on many different positions relative to its “heads” or “tails” hemispheres.
Because each qubit can hold many different states of information, multiple qubits connected through quantum entanglement hold the promise of speedily performing complex computing operations through interference. Currently, that might take thousands or millions of years on modern supercomputers. To build such quantum computers, some proponents have been using lasers and electric fields to trap and manipulate atoms as individual qubits whilst others have been experimenting with qubits made of loops of superconducting metal.
Why quantum mechanics?
Quantum mechanics is perhaps unrivaled as the most fascinating scientific discovery of the 20th century. Modern electronic devices that have changed the world of technology from lasers and magnetic resonance imagers (MRIs) to hard drives and liquid crystal displays (LCDs) owe their existence to the application of quantum mechanics.
The current challenge facing the information processing industry is to make more capable devices that are even smaller. Since the current best processors have approximately 14 billion transistors packed on a chip, the only way to keep improving technology is to reduce the transistor to the size of an atom. The laws of quantum mechanics dominate as the size of matter approach nanoscale sizes. Matter at the atomic level reveals a world wholly unfamiliar to our senses, where atoms can pass through barriers and the act of observing an object can change its state.
What important quantum physics concepts should I know to appreciate how quantum computers work?
The most important concepts in quantum physics are superposition, entanglement, interference, and decoherence.
Superposition gives a quantum qubit possible states that go beyond just digital 1 or 0. The best analogy is a spinning coin where the spin is part of the equation for the state. It is from superposition that we get the exponential growth in the amount of data that can be handled during an active quantum computation. While 1 qubit contains two pieces of information, 10 qubits contain ²¹⁰ = 1024 pieces.
On the other hand, entanglement is a strange concept where two qubits, once they have been entangled will have the same synchronized state even when they are miles apart. Both superposition and entanglement are part of the famous thought experiment of Schrödinger’s cat.
Then, there is interference where the right answer is amplified by the interference of qubit states and wrong answers are canceled out. Interference is mainly a wave phenomenon that serves a very special role in the development of many qubit quantum computers. The power of a quantum processor is such that with enough high quality, usable qubits, we may be able to simulate and solve suitable complex problems.
Decoherence: Due to their small size quantum systems are very sensitive to their surroundings. Composite states due to superposition eventually diminish and finally collapse — and their desired quantum characteristics then disappear. This process is called decoherence and is one of the greatest challenges to be faced in quantum technology. The two forms of coherence are thermal relaxation and depolarisation. Relaxation is usually referred to as T1 and is a measure of how long it takes a
system to spontaneously move to ground state; depolarisation also called T2 which measures how long it takes the system to lose the superposition state. In building a quantum system we have competing interests: isolating the system from its surroundings to avoid decoherence and the need to be able to manipulate the system.
Superconductivity: A superconducting material has zero resistance when cooled below a certain temperature (no wonder why we talk of dilution refrigerators and temperatures around 10–15mK). Superconducting qubits are devices that are fabricated with superconducting materials separated by a thin layer of insulation material (Josephson Junction), operated in their superconducting state where they have well-defined energy levels that can be precisely manipulated.
What is the difference between a quantum computer and a classical computer?
Quantum computers are a radically different kind of computer-based on the laws of quantum mechanics. A classical computer manipulates bits (countless tiny electrical impulses to effect billions of microscopic transistors) to carry out a task whilst in a quantum computer computation is achieved through qubits (precise control of superposition and entanglement of electron spins or currents or polarization of photons).
In 2018, two technologies are used in most quantum computers (trapped ions and artificial “atoms” generated by superconducting circuits), but many different technologies are currently being explored for the basic physical implementation of qubits, or “physical qubits.”
That said, quantum computers have the potential to solve problems that scale up very fast and thus are intractable to classical computers.
Why are we so interested in quantum computers and quantum simulators?
The basic response is that quantum computers have certain problems they can handle much faster than classical computers. Hard problems are not only a question of whether they take a long time — the question is whether they can be solved at all and efficiently with available resources. The class of problems which quantum computation belongs to is called BQP (bounded-error quantum polynomial time).
“A quantum computer could be viewed as the most stringent test of quantum mechanics that we’re going to see in our lifetimes. The case for building QCs would remain strong even if no applications had been found, and even if the applications that have been found turn out not to have great economic importance.” Scott Aaronson
Read on Part 2 here
